Acrylic latices used in the production of printing inks often contain what is called a support resin. These water and alkaline soluble (at pHs of about 8) resins are added to the emulsion polymerization reaction to improve the stability and rheological properties of the latex. Improved stability results from adsorption of the resin on the surface of the particles and the increased viscosity of the emulsion.
High molecular weight emulsion polymers are widely used in the coatings industry. However, several problems are associated with high molecular weight emulsion polymer technology, including: poor wetting of metal and plastic substrates, cratering of resulting films, low gloss or mudcaking of resulting films, wetting and adherency problems, mechanical instability, freeze-thaw instability, shear thinning, and poor physical properties of the resulting film. U.S. Pat. No. 4,839,413 (which is hereby incorporated by reference) attempts to address and overcome these problems by employing hard acrylic resins as support resins.
Such hard acrylic resins have become the support resins most commonly used by the ink industry. However, as these resins are relatively expensive, ink formulators are actively searching for low cost alternatives.
One such alternative is taught by Rivera and Zuraw in commonly assigned U.S. Pat. No. 5,216,064 (which is hereby incorporated by reference). In this patent the authors teach alkali-soluble rosin-based support resins for use in producing emulsion polymer compositions. These compositions are subsequently employed to formulate inks suitable for use in gravure printing. However, the inks taught in this patent have relatively low viscosities and are, therefore, unsuitable for use in flexographic printing applications.
Another alternative to hard acrylic resins is taught by Hutter in the commonly assigned, allowed, patent application Ser. No. 07/987,794 filed Dec. 9, 1992 and now U.S. Pat. No. 5,306,762 (which is hereby incorporated by reference). This application teaches the incorporation of both amide-containing monomers and non amide-containing monomers into the emulsion polymer compositions of U.S. Pat. No. 5,216,064; thereby producing improved ink formulations which exhibit enhanced peel strengths for gravure laminating inks. However, the inks taught in this patent have also proven to be unsuitable for flexographic printing because of low viscosities.
Therefore, it is the object of this invention to utilize low cost alkali-soluble support resins to produce emulsion polymer compositions for use in formulating inks suitable for use in flexographic printing applications.